kernel stack memory

[Ashish Sangwan]

Enable this CONFIG_CC_STACKPROTECTOR and you will get crash.
Stack overflow does'nt necessarily creates kernel panic ;)

On Thu, Sep 13, 2012 at 5:00 PM, Denis Kirjanov <kirjanov at gmail.com> wrote:
> At the moment of forking a new process do_fork() creates a new stack for the
> task by using alloc_thread_info_node():
>
>         struct page *page = alloc_pages_node(node, THREADINFO_GFP,
>                                              THREAD_SIZE_ORDER);
>
>
> On 9/13/12, Rajat Sharma <fs.rajat at gmail.com> wrote:
>> "The kernel stack is part of task_struct of the running process"
>>
>> Please double check that, its not part of task_struct, rather on some
>> architectures, kernel stack is extended by a thread_info structure at
>> the end which keeps a link to task_struct of the process.
>>
>> -Rajat
>>
>> On Thu, Sep 13, 2012 at 1:59 PM, Arun KS <getarunks at gmail.com> wrote:
>>> Hello Shubham,
>>>
>>> On Thu, Sep 13, 2012 at 12:15 PM, shubham sharma <shubham20006 at gmail.com>
>>> wrote:
>>>>
>>>> Hi,
>>>>
>>>> As far as i know, the size of stack allocated in the kernel space is
>>>> 8Kb for each process. But in case i use more than 8Kb of memory from
>>>> the stack then what will happen? I think that in that case the system
>>>> would crash because i am accessing an illegal memory area. I wrote
>>>> kernel module in which i defined an integer array whose size was 8000.
>>>> But still it did not crash my system. Why?
>>>>
>>>> The module i wrote was as follows:
>>>>
>>>> #include <linux/kernel.h>
>>>> #include <linux/module.h>
>>>>
>>>> int __init init_my_module(void)
>>>> {
>>>>         int arr[8000];
>>>>         printk("%s:%d\tmodule initilized\n", __func__, __LINE__);
>>>>         arr[1] = 1;
>>>>         arr[4000] = 1;
>>>>         arr[7999] = 1;
>>>
>>> Instead do a memset.
>>> memset(arr, 0, 8192);
>>>
>>> If you do this the current calling process thread_info will be set to
>>> zero.
>>> This should cause a crash.
>>>
>>> Thanks,
>>> Arun
>>>
>>>
>>>>
>>>>         printk("%s:%d\tarr[1]:%d, arr[4000]:%d, arr[7999]:%d\n",
>>>> __func__,
>>>> __LINE__, arr[1], arr[4000], arr[7999]);
>>>>         return 0;
>>>> }
>>>>
>>>> void __exit cleanup_my_module(void)
>>>> {
>>>>         printk("exiting\n");
>>>>         return;
>>>> }
>>>>
>>>> module_init(init_my_module);
>>>> module_exit(cleanup_my_module);
>>>>
>>>> MODULE_LICENSE("GPL");
>>>>
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>>>
>>>
>>>
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>>
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>
>
> --
> Regards,
> Denis
>
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